A wide variety of organotin compounds has been proposed for use as catalysts in the preparation of polyurethanes. Certain of these are in commercial use, either alone or as co-catalysts with tertiary amine catalysts. In one group of such organotin catalysts the tin atom is tetravalent meaning the tin atom is bonded to 2 hydrocarbon radicals and 2 other atoms which may be oxygen, nitrogen, or carbon. Representative patents showing such dialkyltin catalysts are the following:
U.S. Pat. No. 3,164,557 PA1 U.S. Pat. No. 3,681,271 PA1 U.S. Pat. No. 3,703,484 PA1 U.S. Pat. No. 3,796,674 PA1 UK Pat. No. 899,948
Another family of tin catalysts are the stannous (divalent tin) salts of carboxylic acids which are good "gellation" catalysts for the reactions leading to the formation of polyurethanes. However, these catalysts suffer from poor hydrolytic stability and lack of resistance to oxidation by air and, consequently, they must be stabilized by the addition of antioxidants and stored under an atmosphere of dry nitrogen.
Patents disclosing certain amido divalent metal carboxylates include U.S. Pat. Nos. 2,820,053 and 3,365,477.